7 Reasons Why Wood is a Better Environmental Choice than Other Building Materials

Often overlooked in a contemporary Malaysian built environment dominated by reinforced concrete and, to a lesser extent, steel structures, this article makes the case for revisiting timber as a more environmentally mature construction material. It begins by setting out the green credentials of trees and the wood-based products which we derive from them, before going on to explain their long-term ability to sequester carbon and relatively low environmental impact.

Wood has been used throughout the history of mankind and has provided humans with a broad range of building materials and products. Arguably, wood gives "fingerprints" in our buildings and these "fingerprints" allow our built environment to connect us to nature (Figure 1). A study by Planet Ark (2015) entitled "Wood - Housing, Health, Humanity" finds that "being surrounded by wood at home, work or school has positive effects on the body, the brain and the environment..." and "...the presence of wood has positive physiological and psychological benefits that mimic the effect of spending time outside in nature." 

Figure 1: Wood gives Mother Nature's fingerprints in our buildings

Given the above, it makes sense if many more of the buildings which we construct in the future are made of wood. Over the next 20 years, three billion people (or 40% of the world's population), will need a new home (UN-Habitat, 2011). Today, half of us live in cities, and by 2040, that number is going to grow to 75%. One in three people, or over one billion people, living in cities today are living in slums and a further one hundred million people are homeless. The challenge for developers, architects, engineers, and society, in general, is to find a solution to house all of these people and, perhaps more importantly, doing so in a sustainable manner. 

Unfortunately, our construction materials of choice today are steel and concrete and whilst these materials have their benefits, they do not come from renewable sources. They also contribute to climate change as they require a great deal of energy for their production and they entail higher greenhouse gas (GHG) emissions. The production of steel contributes to about 3% of man's GHG emissions, and that of concrete to over 5%. With an alarming 8% of our contribution to GHGs today coming from those two materials alone, we urgently need to find an environmentally benign material to replace them or reduce our reliance on them, in the construction of buildings. 

The building sector is also a major contributor to climate change and is the largest energy-consuming sector, according to the International Energy Agency (2013), accounting for over one-third of final energy consumption globally and an equally important source of carbon dioxide emissions. This is largely the result of fossil fuels being used to generate electricity for buildings. Furthermore, about 65% of the building sector's GHG emissions come from residential buildings, while commercial buildings account for the remaining 35%. It is clear from the above that if we continue to use the methods we used in the past to solve the housing needs of these additional three billion people, we will be on a head-on collision course with climate change (Figure 2). 

Figure 2: How we solve the problem to house the world’s population that needs a home is a head-on collision with climate change

That is why we have to start thinking in new ways. Over the past decade, the concept of green building design and construction has become mainstream and we are increasingly aware of the potential environmental benefits of alternatives to conventional construction. Much of the focus of green building design has been on reducing a building’s energy consumption and reducing its negative impact on our health and well-being. However, choosing building materials with low environmental impact is also a major area of focus. The building sector has a great opportunity to reduce GHG emissions and tackle climate change, and increasing the use of wood products in construction is part of the solution.

Here are the 7 reasons why:

1. Wooden Buildings and Products Store Carbon Indefinitely

The role of carbon emissions in global climate change and its negative impact on ecosystem sustainability and the general health of our planet has never been more universally understood. Wood is the only construction material grown naturally using the sun's power. Forests play a major role in the Earth’s carbon cycle and we all know that forests help to clean the air by absorbing carbon dioxide and releasing oxygen. The carbon absorbed is stored until the tree dies, at which point the carbon is either released back into the atmosphere or absorbed into the forest floor. When a tree burns, it also releases its carbon back into the atmosphere.

However, when trees are felled to produce timber products to be used in buildings or made into furniture, the timber in that building or piece of furniture will continue to store carbon for as long as it exists. A recent survey conducted by campaign partner Forest and Wood Products Australia (Planet Ark, 2011) showed that although 93% of people understood that trees absorb carbon, only 39% realised that wood's vital role is carbon sequestration.

Wood stores carbon dioxide in the form of carbon. In fact, one-half the dry weight of wood is carbon. One cubic metre of wood contains one tonne (1000kg) of carbon. If we substitute a cubic metre of wood for other construction materials (concrete, blocks or bricks), we will save approximately one tonne of carbon from being emitted into the atmosphere (Reid et al., 2004) (Figure 3). 

If we built a 20-story building out of cement and concrete, the manufacturing process would release 1,200 tonnes of carbon dioxide into the atmosphere. However, if we built it in wood, we would sequester about 3,100 tonnes of carbon. The net difference of 4,3000 tonnes of carbon is the equivalent of removing around 900 cars from the road in one year. Considering that over the next 20 years, three billion people in the world will need a new home, the use of wood in construction could be a major contributor to reducing carbon emissions. A study by Oliver et al. (2014) titled “Carbon, Fossil Fuel, and Biodiversity Mitigation with Wood and Forests” states that building with wood could reduce annual global emissions of carbon dioxide by 14-31%. 

Figure 3: Replacing one cubic metre of other building materials with one cubic metre of wood could save up to one tonne of carbon emissions

Two of the most pressing climate change considerations are: finding ways to reduce our carbon emissions and to store, or sequester, carbon, and wood is the only natural building material that does both of these. The ability of wood to store large quantities of carbon for long periods of time sets wood apart from and provides a significant advantage over other building materials such as steel and concrete. Mass timber may not be suitable for every project and will not solve our cities' housing crisis alone, but it should be considered a major contribution. 

2. Wooden Products Have Less Embodied Energy

Embodied energy refers to the quantity of energy required to harvest, mine, manufacture, and transport to the point of use of a material or product. Wood, a material that requires minimal energy-based processing, has a low level of embodied energy relative to other materials (Figure 4). Solid-sawn wood has the lowest level of embodied energy; wood products requiring more processing steps (such as plywood and engineered wood products) require more energy to produce but still require significantly less energy than their non-wood counterparts. This is because trees use the sun's energy to grow, and relatively little additional energy is needed to transform trees into wood-based products, giving them a very low carbon footprint when compared to other construction materials.

Figure 4: Levels of embodied energy for materials used in the average Australian house

Source: CSIRO (2003).

Historically, a building’s operational phase has accounted for the greatest energy consumption during the building’s lifetime, mainly for space heating and cooling purposes. However, we are increasingly concerned with the embodied energy of materials because this is no longer the case for energy-efficient buildings or zero-energy buildings. A life cycle energy analysis (LCEA) research conducted by Crawford (2012) concludes that embodied energy becomes more significant, relative to operational energy, as operational energy is reduced (through efficiency improvements and lifestyle changes).

3. Wooden Buildings Have Low Life Cycle Environmental Impacts

Performance of materials is measured through life cycle assessment (LCA), which considers the environmental impact of materials, assemblies and even whole buildings, over the course of their entire lives – from extraction/harvesting through manufacturing, transportation, installation, use, maintenance and disposal or recycling (Figure 5). Study after study has shown that wood outperforms other materials when considered over its lifetime using LCA.

Figure 5: Full life cycle assessment for a material, assembly or whole building

One study conducted by the Canadian Wood Council (1997) compared the life cycle environmental impacts of 50,000 square-foot office buildings constructed using wood, steel and concrete as the main structural materials. The results show that wood outperforms both materials in terms of energy use, GHGs, air pollution, solid waste and ecological resource impacts (Figure 6). Numerous other studies have reached the same conclusion: wood buildings offer clear environmental advantages.

Figure 6: Wood outperforms both steel and concrete in terms of all environmental impacts

Source: Forestry Innovation Investment (2017).

4. Wood is a Natural Insulator

Wood also contributes to energy efficiency because its cellular structure contains air pockets that limit its ability to conduct heat, thus making it a better insulator than other materials – 400 times better than steel and 15 times better than concrete. More insulation is needed for steel and concrete to achieve the same thermal performance.

5. Wood Produces Minimal Waste

In green building discourse, the three Rs – reduce, reuse and recycle – have become a mantra for the responsible use of resources. Very little, if any, waste is generated during the manufacturing of wood and wood-based products, as almost all by-products are used, whether as raw materials or as an energy source. During the production of sawn timber, the off-cuts, wood chips and sawdust generated can be used on-site to produce clean bio-energy, replacing fossil fuels and further reducing emissions. They are also used off-site for the production of particleboard or for the pulp and paper industry (Figure 7). In North America, some wood producers are able to use 99% of every tree harvested.

Figure 7: Wood produces minimal waste during its entire life cycle

Source: Metsa Wood (2017)

At the end of a building’s life, its wood can be recovered and reused in construction as wood requires little energy to be salvaged. In contrast, when concrete is broken up, it is impossible to reuse it for construction. Steel requires a massive amount of energy to melt it to reuse it, and that melting process requires burning fossil fuels. Even with high rates of recycled content, steelmaking remains one of the most energy-intensive and environmentally damaging industries. 

6. Wood is a Renewable Resource

The fourth R - renewal - is also an important part of the conservation mantra. Unlike many building materials, wood does not deplete the earth of its natural resources. Because wood is produced with the sun's natural energy, it is endlessly renewable as it can be grown and harvested over and over again. 

However, in order for wood to be a truly renewable resource, sustainable forest management must be practised. This will help to ensure that forests are legally harvested and managed to meet society’s long-term demand for forest products, whilst adhering to the following 3 pillars of sustainable development:

• Ecological - protecting the biodiversity and ecosystems provided by the forests and mitigating some of the effects of climate change
• Economic - reducing rural poverty
• Socia-cultural - safeguarding local livelihoods

Unfortunately, sustainable forestry practices are not always applied. For this reason, it is the responsibility of architects, product designers, material specifiers and homeowners to always choose wood products certified to be sustainable. 

7. Wood Helps Earn Points in Green Building Rating Systems

Specifying wood can also contribute points in categories typically found in existing green building rating systems such as the US Leadership in Energy and Environmental Design (LEED), UK's BRE Environmental Assessment Method (BREEAM) and Malaysia's Green Building Index (GBI). The categories include:  

• Certified wood 
• Recycled/reused/salvaged materials: Wood products that qualify for “Materials with Recycled Content” include finger-joined studs, medium-density fibreboard, and insulation board
• Local sourcing of materials
• Waste minimization
• Indoor air quality: Many wood adhesives, resins, and engineered and composite products contain no added urea formaldehyde and have strict limits on VOC content.
• Advanced building techniques and skills (e.g. advanced framing)

All green building rating systems also consider the energy consumption during the period that the building is in use. However, it is important to note that only a few (such as LEED and BREEAM) take account of the construction materials’ impact on the climate or consider the production phase for the materials used in a building from a life cycle perspective. 

References:

1. Canadian Wood Council (1997). A Case Study Comparing the Environmental Effects of Building Systems, Wood the Renewable Resource, No. 4, 1-11.
2. Crawford, R.H. (2012). Report on Life Cycle Energy Analysis.
3. International Energy Agency (2013). Report on Transition to Sustainable Buildings: Strategies and Opportunities to 2050.
4. Oliver, C.D., Nassar, N.T., Lippke, B.R. & McCarter, J.B. (2014). Carbon, Fossil Fuel, and Biodiversity Mitigation with Wood and Forests, Journal of Sustainable Forestry, Vol. 33(3), 248-275.
5. Planet Ark (2011). Wood - A Growing Answer to ClimateChange.
6. Planet Ark (2015). Report on Wood: Housing, Health, Humanity.
7. Reid, H., Huq, S., Inkinen, A., MacGregor, J., Macqueen, D., Mayers, J., Murray, L. & Tipper, R. (2004). Report on UsingWood Products to Mitigate Climate Change: A Review of Evidence and Key Issuesfor Sustainable Development. International Institute for Environment andDevelopment, London. 
   
8. UN-Habitat (2011). State of the World's Cities 2010/2011 - Cities for All: Bridging the Urban Divide. UN-Habitat: Nairobi. 

Author's Note:

After being posted, this article was accepted for publication as the first half of a chapter in a book titled "Greening Malaysia" by Pertubuhan Arkitek Malaysia (PAM). 

For full citation: Shari, Z. (2017). Why Not Wood: A Case Engineered Timber Construction in Malaysia. In M. Gelber, B.C. Wee, S. Hijjas (Eds.), Greening Malaysia (pp.254-263). Kuala Lumpur: Pertubuhan Arkitek Malaysia (PAM).